In the course of making castings, for example, the crankcase of an internal combustion engine, it is often necessary to have cored holes in the finished casting as a result of the need to support internal cores, for example, for the cores performing the coolant passages, during the casting process. These cored holes generally are required to be sealed, especially if they are in the side of the crankcase but often even when located in the top deck of the crankcase which interfaces with the cylinder head gasket and cylinder head.
A conventional method of sealing cored holes is to first machine a counterbore and then press a metal cup plug which is retained against the machined side walls of the castings by an interference fit. Another method is to insert a Welch or expansion plug, a concave disk, in the machined bore and flatten out the disk as shown in Welch U.S. Pat. No. 1,058,210. However, each of these methods requires a machined counterbore since these metal plugs will not seal an as-cast surface. Additionally, as a practical matter, the holes have to be circular and an as cast hole may not be circular especially if the mold parting line passes along a diameter of the hole.
It is also known to seal holes of various types with elastomeric plugs, for example, those shown in U.S. Pat. Nos. 3,200,984, 3,578,027, 4,287,996, and 4,736,865. However, such plugs generally held in place by the compression of the elastomeric material against the side walls and are more susceptible to being blown out by internal pressure, for example, the coolant pressure in the crankcase, especially if installed in a tapered hole as might result from the draft angle of an as-cast hole.